Stereochemistry of C-6 Nucleophilic Displacements on 1, 1

J. Org. Chem. , 2004, 69 (22), pp 7653–7660. DOI: 10.1021/ ... A practical and expeditious approach to 1 was derived from these new results. View: P...
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Stereochemistry of C-6 Nucleophilic Displacements on 1,1-Difluorocyclopropyldibenzosuberanyl Substrates. An Improved Synthesis of Multidrug Resistance Modulator LY335979 Trihydrochloride Charles J. Barnett,*,† Bret Huff,* Michael E. Kobierski, Michael Letourneau, and Thomas M. Wilson Chemical Product Research and Development Division, Lilly Research Laboratories, A Division of Eli Lilly and Company, Indianapolis, Indiana, 46285 [email protected]; [email protected] Received June 6, 2004

Studies of the displacement chemistry of 1,1-difluorocyclopropyldibenzosuberanyl alcohol 4 and its activated bromide derivative 6 have led to an improved approach to anti-2, a key precursor to LY335979 3HCl (1). Bromination of either syn-4 or anti-4 gave anti-oriented 6, indicating thermodynamically controlled product stereochemistry via a stabilized 1,1-difluorohomotropylium ion intermediate. Reaction of 6 with piperazine proceeded irreversibly to provide an isomeric mixture of piperazine products, with the syn:anti product ratio increased by solvent effects. Reaction of 6 with pyridine and pyrazine, on the other hand, gave anti-pyridinium and pyrazinium salts, respectively, apparently via equilibration of initially formed syn products. Reduction of pyrazinium salt 11 with lithium borohydride/TFA provided anti-2 unaccompanied by its syn isomer. A practical and expeditious approach to 1 was derived from these new results. Introduction

SCHEME 1

The development of multiple drug resistance is a serious limitation on the effectiveness of many oncolytic drugs. New findings on the biological basis of multiple drug resistance have permitted the rational search for modulators of specific resistance pathways.1 Compound LY335979 3HCl (1) has been found to be a clinically useful modulator of P-glycoprotein-mediated multiple drug resistance in research beginning at the former Syntex Corporation and continuing2 at Lilly Research Laboratories.3 The expansion of clinical trials prompted us to embark on a program to create a practical and costeffective synthetic approach to 1.

similar structure saturated in place of the difluorocyclopropyl group in 1. LY335979‚3HCl was first prepared at Syntex as part of an effort to improve upon the activity of MS-073,4 a †

Retired June 30, 2001. Current address: 1305 Brickmill East, Mount Pleasant, SC 29466-7919. (1) Norman, B. H. Drugs Future 1998, 23, 1001-1013. Ford J M.; Hait, W. N. Pharmacological Reviews 1990 42, 155-99. (2) LY335979‚3HCl was licensed from Syntex Corporation in November, 1994. The Syntex serial number was RS-33295-198.

The Syntex strategy5 for the synthesis of 1 is indicated retrosynthetically in Scheme 1. One key disconnection was at the C-N bond joining the substituted piperazinyl moiety to the chiral 2-hydroxypropoxyquinoline linker via the substituted piperazine 2 possessing the required anti stereochemistry6 and the known7 (R)-epoxide 3. Although other approaches could be envisioned, this one provided the greatest

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Barnett et al. SCHEME 2

convergence and relied upon the opening of an epoxide by an amine, a well-known and stereochemically reliable reaction. On the other hand, the synthesis of anti-2 as described by the Syntex group was encumbered with relative stereochemical problems as indicated in Scheme 2. Chlorination of syn-4 (SOCl2) provided a mixture of chlorides 5 in an anti:syn ratio of about 90:10.8 Reaction of the mixture with formylpiperazine, however, unfortunately gave rise to a nearly equal mixture of piperazinyl isomers anti-7 and syn-7 (anti:syn 55:45).9 The mixture could be separated by chromatography, providing purified anti-7, which gave anti-2 upon deprotection with strong base. Although it was possible to utilize the original approach to anti-2 for the preparation of relatively small quantities of LY335979, the unfavorable impact of ambiguous stereochemistry of the piperazine displacement step on efficiency of the synthesis quickly became apparent. We describe herein studies leading to successful resolution of the stereochemistry issue, leading to an expeditious approach to 1 suitable for commercial scale use. Stereochemical Studies Synthesis of Bromide 6 from syn-4. We found the bromination of dibenzosuberanol syn-4 to be the method of choice for activating the molecule for amine displacement. Attempted preparation of sulfonate esters of syn-4 failed to give useful products, apparently because of the instability of these intermediates. As mentioned previously, chlorination with SOCl2 provided a mixture of stereoisomeric chlorides and was not otherwise advanta(3) For an excellent review of the biological research on LY335979, see: Dantzig, A. H.; Law, K. L.; Cao, J.; Starling, J. J. Curr. Med. Chem. 2001 8, 39-50. (4) (a) Sato, W.; Fukazawa, N.; Suzuki, T.; Yusa, K.; Tsuruo, T. Cancer Res. 1991, 51, 2420-4. (b) Suzuki, T.; Fukazawa, N.; San-nohe, K.; Sato, W.; Yano, O.; Tsuruo, T. J. Med. Chem. 1997, 40, 2047-2052. (5) (a) Pfister, J. R.; Makra, F.; Muehldorf, A. V.; Wu, H.; Nelson, J. T.; Cheung, P.; Bruno, N. A.; Casey, S. M.; Zutshi, N.; Slate, D. L. Bioorg. Med Chem Lett. 1995, 5, 2473-2476. (b) Pfister, J. R.; Slate, D. L. U.S. Patent 5,643,909, 1997. (6) For this article we define the relative stereochemistry in all structures related to 2 as anti on the basis of the relatively opposite positions of the cyclopropyl and C-6 substituent groups with respect to the dibenzocycloheptane ring. Syn refers to the orientation of these groups on the same side of the dibenzocyloheptane ring. (7) Fukazawa, N.; Suzuki, T.; Kawauchi, N.; Komatsu, H.; Otsuka, K.; Nakajima Y. U.S. Patent 5,463,61, 1995. (8) The anti:syn ratio of chlorides 5 was determined by repeating the reported experiment from ref 5b. (9) The anti:syn ratio for the isomeric mixture of 7 was determined by HPLC of the crude product as a part of this work. A ratio of these isomers of anti:syn 52:48 after chromatographic separation was reported by Syntex (ref 5b).

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SCHEME 3

geous. Reaction of 4 with either phosphorus tribromide in halogenated hydrocarbon solvents or, preferably, 48% aqueous HBr, however, gave crystalline dibenzosuberanyl bromide 6 (Scheme 2) as a single, anti stereoisomer in high yield. The formation of 6 represented apparent inversion of the configuration of the hydroxyl-bearing center, but the cyclopropyldibenzosuberane-based structures of this series suggested the possibility of stabilized cationic intermediates instead of an SN2 mechanism. The reaction sequence shown in Scheme 3 was carried out in order to clarify the mechanism of the formation of 6. Reaction of syn-4 with benzoic acid under Mitsunobu10 conditions gave, after purification, anti-8. The assignment of anti stereochemistry to the product was supported by NMR data that showed no NOE at the cyclopropyl hydrogens upon irradiation of the C-6 proton. In contrast, the isomeric benzoate syn-8, prepared by esterification of syn-4 with benzoic anhydride, clearly showed a NOE between the cyclopropyl and C-6 protons. Hydrolysis of anti-8 with sodium hydroxide in methanol gave the previously unreported anti-4. Reaction of anti-4 with phosphorus tribromide under the conditions described for conversion of syn-4 to 6 gave anti-bromide 6 as the only product with apparent retention of configuration. These results clearly indicated that the stereochemical outcome of bromination of syn-6 was not caused by Walden inversion and was best explained by an SN1 mechanism involving the fluorinated dibenzohomotropylium ion11 intermediate 9 (Scheme 3). Thus formation of 6 occurred under thermodynamic control by (reversible) attack of bromide ion on 9, and (10) Hughes, D. L. Org. React. 1992, 42, 335-656. (11) For a definitive paper on the chemistry of the dibenzohomotropylium ion, see: Childs, R. F.; Brown, M. A.; Anet, F. A. L.; Winstein, S. J. Am. Chem. Soc. 1972, 94, 2175-2183 and references therein.

Improved Synthesis of LY335979 Trihydrochloride

any of the kinetically formed syn-bromide was apparently rapidly equilibrated to 6 via reversion to 9. These results provided a framework for understanding the displacements of amine nucleophiles on 6. Displacements on 6 by Nitrogen Nucleophiles. A 3-fold excess of piperazine was successfully substituted for the much more expensive formylpiperazine in the preparation of anti-2 without reduction in yield or formation of bis-substituted piperazine byproducts,12 albeit with no effect on the ratio of piperazine products. These results shortened the synthesis of anti-2 by obviating the protection and deprotection of the essential reagent, piperazine. The resulting isomeric mixture of piperazine products 2 were, however, not easily separated by preparative HPLC. We have previously reported an alternative, nonchromatographic separation scheme in which the gross amount of unwanted syn-2 was removed by crystallization of the free base mixture from acetonitrile and the resulting enriched mixture was converted to the hydrochloride or hydrobromide salts and crystallized from dichloromethane.13 Recrystallization from dichloromethane provided purified anti-2 as its salt (anti: syn 99.5:0.5) in about 32% overall yield from bromide 6. Formation of the isomeric piperazines was not reversible. Exposure of each of the isomers of 2 separately to the conditions of piperazine displacement in acetonitrile returned the compounds unchanged. We surmised that the reaction of 6 with piperazine resulted in almost indiscriminate, irreversible attack on the homotropylium ion 9 in view of the results of the foregoing study of the stereochemistry of formation of bromide 6. We hoped to influence the relative rates of the competing reactions by varying the reaction medium. The results of a study of solvent effects on the displacement of bromide 6 by piperazine are shown in Table 1. A very slight concentration effect was noted in acetonitrile (entries 1-3), with the product ratio only slightly more favorable at lower concentrations. Acetonitrile, the standard solvent choice, proved to be the best for favoring anti-2. Other solvents examined gave less favorable anti: syn ratios, and tetrahydrofuran provided a good (relative) yield of the undesired syn isomer. A search of the literature did not uncover any reports of reactions of other nitrogen heterocycles with dibenzocyclopropylsuberanyl halides. The following serendipitous experiment proved, however, to be very illuminating. Compound syn-4 was reacted with piperazine in toluene in the presence of pyridinium tosylate in an effort to prepare piperazines 2 by direct displacement on 4, thus precluding the activating step of bromination. The reac-

TABLE 1. Solvent Effects on the Stereochemical outcome of the Reaction of 6 with Piperazine

entry

solventa

2, anti:syn

1 2 3 4 5 6 7 8 9 10 11 12 13

acetonitrile, [6]init 0.125 M acetonitrile, [6]init 0.208 M acetonitrile, [6]init 0.62 M acetone isopropyl alcohol ethyl acetate methanol ethanol dimethyl formamide chloroform toluene tert-butyl methyl ether tetrahydrofuran

55:45 54:46 42:58 41:59 40:60 39:61 36:64 35:65 34:66 34:66 26:74 26:74 15:85

a Initial concentration of 6 was 0.156 M except as noted. For details see Experimental Section.

tion failed to provide useful amounts of desired products, but a single pyridinium tosylate was isolated in 18% yield. The analogous pyridinium bromide (anti-10, below) was obtained in quantitative yield, as a single stereoisomer, when bromide 6 was reacted with pyridine in chloroform at 57 °C. The following NMR experiment allowed assignment of anti stereochemistry to the product of the foregoing reaction. Bromide 6 was dissolved in pyridine-d5 and the resulting process was followed, initially at 27 °C. The relative configuration of the initially predominant product (syn-10) was assigned from observation of a NOE enhancement between the cyclopropyl fusion and C-6 protons. As the temperature was increased from 27 to 47 °C; however, the initial product was replaced by a new component that showed a similar proton NMR spectrum but lacked the NOE observed in the early product. Thus, structure anti-10 was assigned to the final, more stable product.14 These results are in accord with observations reported by Winstein et al.15 of the solvolyses of the acetate esters of didesfluoro-4 in which a syn-oriented product predominated (under kinetic control) regardless of the relative stereochemistry of the starting materials. This is, to our knowledge, the first example of a reaction involving a dibenzohomotropylium species in which an initially formed syn displacement product is equilibrated to the (isolated) anti isomer.

(12) A sample of the potential side product, N,N-dialkylated piperazine i (stereochemistry not determined), was prepared by reaction of 2 and 6 and determined not to be detectable in the purified product, 2, by HPLC analysis.

(13) Astleford, B. A.; Barnett, C. J.; Kobierski, M. E.; Wilson, T. M. U.S. Patent 6,570,016, 2003. Astleford, B. A.; Barnett, C. J.; Kobierski, M. E.; Wilson, T. M. U.S. Patent 6,624,304, 2003.

(14) After 2 days at 57 °C, none of the initial product (syn-10) could be observed by NMR.

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entry

solvent

1 2 3 4 5 6 7

none DMSO DMSO-CH2Cl2 (1:9) DMF CH3CN CH2Cl2 THF

pyrazine temp reaction yield molar excess (°C) time (h) (%) 3.0 3.0 3.0 6.0 3.0 6.0

110 37 30 70 75 25 55

0.5 4 25 4.5 24 4 23

91a 93a 88a 60 25 18a 0

a Isolated yield. Experiments 4, 5, and 7 were carried out in a NMR tube in the indicated deuterated solvent. Yields for 4, 5, and 7 are given as ratios of starting material to product at the indicated time.

As expected, reaction of bromide 6 with neat pyrazine also provided the desired anti-difluorodibenzosuberanylpyrazinium bromide16 (11), further confirming the stereochemical course of the reaction. In contrast to the pyridine experiment, however, the corresponding synoriented product was not observable by NMR, suggesting a relatively rapid equilibration of the isomeric products. Importantly, no bis-pyrazinium products could be detected in the isolated product. A number of solvents were screened for the reaction, and the results are summarized in Table 2. DMSO clearly provided best results for the pyrazine displacement, but addition of cosolvents to the DMSO reactions did not have a deleterious effect on the rate or yield. Synthesis of LY335979‚3HCl As a result of the preceding studies we have developed a convenient, stereoselective, and scalable approach to 1 by incorporating pyrazine in place of piperazine for the incorporation of the piperazine ring as depicted in Scheme 4. Optimization of Cyclopropanation. The implementation of this synthetic plan relied on an efficient and reliable method for the difluorocylopropanation of dibenzosuberanone (12). Alternative methods to the previously disclosed chlorodifluoroacetate pyrolysis5 were examined. We found that lower-temperature methods, such as dehalogenation of dibromodifluoromethane with zinc or triphenylphosphine, and the reaction of methyltrifluoromethylstannane with sodium iodide17 all failed to effect difluorocyclopropanation on the relatively electron-poor olefinic bond of 12 while reported examples were easily repeated. We concluded that difluorocyclopropanation of (15) See ref 11. (16) Huff, B. E.;, LeTourneau, M. E.; Wilson, T. M.; Bush, J. K,; Reutzel-Edens, S. M. U.S. Patent 6,521,755, 2003. (17) For a review of these and other difluorocyclopropanation methods, see: Brahms, D. L. S.; Dailey, W. P. Chem. Rev. 1996, 96, 1585.

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12 required the high-temperature conditions of chlorodifluoroacetate pyrolysis. We made several improvements to the Syntex difluorocyclopropanation protocol that made it more efficient and amenable to large-scale use. For example, large stoichiometric excesses (15-25 equiv) of alkali salts of chlorodifluoroacetic acid had been required in the original process to drive the reaction substantially to completion at the reported reaction temperature (160 °C). Although the yield as calculated on the consumption of 12 was acceptable at 60-70%, the very poor conversion of the (anhydrous) chlorodifluoroacetate salt caused the process to become unacceptably expensive. Additionally, the nonproduct-forming decomposition of excess carbene reagent generated copious amounts of gaseous and solid waste. We considered this problem to be one of competition between product-forming difluorocarbene insertion to the target olefin and many potential side reactions involving difluorocarbene: oligomerization to tetrafluoroethylene and its insertion products, higher polymers, and reactions with solvent.18

In preliminary experiments we observed that the amount of excess lithium19 chlorodifluoracetate required for complete consumption of 12 was inversely proportional to reaction temperature and directly proportional to the rate of addition of the solution of chlorodifluoroacetate salt. Thus, the rates of product formation (k2) and other carbene processes (k1) converged as temperature was increased, improving the competitiveness of difluorocyclopropanation. Slower addition rates increased the instantaneous ratio of difluorocarbene to available olefin substrate, thus favoring product formation (k2). There were, of course, practical boundaries on both of these improvements. Accelerated rate calorimetry experiments indicated that 13 begins to undergo decomposition at 220 °C. Additionally, the concentration effect attributable to slow addition rates diminished as the concentration of 12 was reduced by the progress of the reaction. For pilot plant scale processing we obtained good results at tem(18) Detailed analysis of the byproducts was not carried out. The volatile fraction was presumed to consist of tetrafluoroethylene and, perhaps, hexafluorocyclopropane, and perfluorocyclobutane. A solid residue remained in the vessel with empirical formula CF2, indicating that it was a polymer of tetrafluoroethylene. The various reactions of difluorocarbene that form these compounds have been documented. See: Birchall, J. M.; Fields, F.; Haszeldine, R. N.; McLean, R. J. J. Fluorine Chem. 1980, 15, 487. (19) Sodium chlorodifluoroacetate was used in earlier examples of this reaction (ref 5; Beard, C.; Berkoz, B.; Dyson, N. H.; Harrison, I. T.; Hodge, P.; Kirkham, L. H.; Lewis, G. S.; Giannini, D.; Lewis, B.; Edwards, J. A.; Fried, J. H. Tetrahedron 1969, 25, 1219 and references therein). Our preference for the lithium salt was based on its increased solubility in the reaction medium. The resulting increased reaction concentration favored product formation and afforded better yields based on ClF2CCO2Li. (See Experimental Section.)

Improved Synthesis of LY335979 Trihydrochloride SCHEME 4

peratures of about 180 °C20 and using a 5.6-fold molar excess of lithium chlorodifluoroacetate. We were able to reduce the intermediate ketone 13 to syn-4 without isolation, effecting a substantial improvement in cycle time. Thus, addition of 5.6 equiv of lithium chlorodifluoroacetate over 11.5 h at 180 °C provided the desired ketone 13, which was converted to syn-4 in situ with aqueous sodium borohydride in 70% overall yield from 4. Synthesis of anti-2. Reaction of syn-4 with 48% HBr in dichloromethane with azeotropic removal of water conveniently provided a solution of bromide 6 in dichloromethane. Addition of pyrazine and DMSO and further reaction gave crystalline pyrazinium bromide 11, precipitated from the reaction mixture after dilution with ethyl acetate in 88% overall yield from syn-4. Reduction of the pyrazinium ring of 11 was required to assimilate this molecule into the synthesis of 1. Catalytic hydrogenation conditions, even in the presence of added acid, were unsatisfactory as poor yields and difficult purification of the product were encountered.21 Fortunately, lithium borohydride reduction of 11 in the presence of trifluoroacetic acid (TFA) gave much better results. The progress of the reduction and evolution of hydrogen could be conveniently controlled by the rate of introduction of borohydride into the reaction mixture. It was therefore possible to carry out the reaction at pilot plant scales with adequate control. The crystalline hydrochloride of anti-2 was obtained by HCl treatment of the product in ethyl acetate in 70% yield from 11. Final Steps. Epoxide 3 was readily prepared by reaction of commercially available 5-hydroxyquinoline (14)22 with glycidyl nosylate by a modified procedure utilizing potassium tert-butoxide in THF as base. As a practical matter, the choice of (R)-glycidyl nosylate as a (20) We were constrained to reaction temperatures of 180 °C or less at pilot plant scale because of reaction safety and vessel heating system limitations. For laboratory experiments a reaction temperature of 210 °C was preferred. (21) There was some evidence (from analysis of side products) for self-condensation of partially reduced pyrazine intermediates, but none of these products were completely characterized. (22) Purchased from Orgasynth (France).

reagent for the glycidylation might be questioned because of its relatively high price. The alkylation of glycidyl derivatives by arylalkoxide ions is, however, subject to racemization due to competing Payne-type epoxide opening (followed by reclosure of the epoxide) by intramolecular displacement of the leaving group. As the classic studies by McClure23 and Sharpless24 elegantly showed, the amount of racemization observed is inversely dependent upon leaving group reactivity in displacements of glycidol derivatives. Our own studies25 of the reactions of chiral glycidol derivatives with 5-hydroxyquinoline indicated that glycidyl nosylate was the best reagent for this purpose, in agreement with the Syntex results. The synthesis was easily completed from the key intermediates 2 and 3 by a modified version of the Syntex procedure. Piperazine 2 hydrochloride was converted to the free base with sodium carbonate in ethanol and reacted with epoxide 3 in acetonitrile without isolation. The reaction mixture was filtered through silica gel and then concentrated, and 1 was obtained as a crystalline salt by addition of ethanolic HCl in 74% yield. Summary We have established that nucleophilic displacement reactions on 1,1-difluorodibenzosuberanyl substrates relevant to the synthesis of LY335979 proceed via the corresponding homotropylium ion intermediate 9. Halogenations give predominately or exclusively anti-halide derivatives under thermodynamic control. Displacements by cyclic amines provide different stereochemical outcomes, depending on oxidation state. Piperazine displacements lead to irreversibly formed mixtures of isomers, (23) McClure, D. E.; Arison, B. H.; Baldwin J. J. J. Am. Chem. Soc. 1979, 101, 3666. (24) (a) Klunder, J. M.; Onami, T.; Sharpless, K. B. J. Org. Chem. 1989, 54, 4(6), 1295-1304. (b) Sharpless, K. B.; Onami, T. H. PCT Int. App. WO 8800190 A1, 1988. (25) Reaction of 5-hydroxyquinoline with (R)-glycidyl nosylate gave about 2% racemization in our hands as found by chiral HPLC analysis of the crude product. Optical purity was restored, however, by crystallization of the product (3) during isolation. Overall stereochemical outcomes for this reaction were in agreement with the Syntex results.5

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whereas pyridine and pyrazine, on the other hand, afforded the anti heteroarenium salts with demonstrated equilibration of the initially predominant syn products. We have exploited the novel pyrazine displacement process (6 f 11) and several other innovative improvements to establish a highly efficient and practical route to LY335995 from dibenzosuberenone (12).

Experimental Section (1aR,6R,10bR)-1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclohepten-6-ol (syn-4). A mixture of dibenzosuberenone (12,5 10.0 Kg, 48.5 mol) and 50 L of triglyme was heated to 180 °C. To this mixture was added a 50 wt % solution of 65 L (272 mol, 5.6 equiv) of lithium chlorodifluoroacetate in glyme at a rate of 0.5 equiv/h until less than 2.0% of the dibenzosuberenone was present by GC analysis (JW Scientific DB-1 methyl silicate 30 m × 0.25 mm column, 20 min run time, initial temp 150 °C, final temp 250 °C). The mixture was cooled to 35-45 °C over 2 h and was treated with 8.0 Kg of Hyflo26 followed by 20 L of ethyl acetate. After stirring for 30 min, the suspended solids were removed by filtration through a prewetted (EtOAc) 7.0 Kg Hyflo plug and washed with 80 L of ethyl acetate. The combined filtrate and washes were distilled at 25-30 °C and 100 mmHg to a volume of approximately 60 L. To this solution of ketone 14 was added a 12 wt % solution of sodium borohydride in aqueous 14 M sodium hydroxide (5.3 Kg, 16.8 mol) over 1 h while maintaining the temperature below 40 °C. The reaction mixture was stirred at 20-25 °C for 3 h, at which time GC analysis (see above for conditions) showed less than 1% of 14. A mixture of 50 L of water, 35 L of methanol, and 6.2 Kg of concentrated HCl was added over 40 min while maintaining the reactor temperature between 25 and 35 °C. The neutralized mixture was stirred for 45 min, and the precipitate was filtered, washed twice with 50 L of water followed by 30 L of methanol, and dried in a filter dryer at 45-50 °C. The crude product was reslurried in 65 L of methylene chloride for 35 min at 20-25 °C and 1 h at 0-5 °C on the filter dryer. The solid was filtered, washed with 25 L of cold methylene chloride followed by 2 × 20 L of cold heptane, and dried in a filter dryer at 45-50 °C to give 9.5 Kg (75%) of syn-4, mp 233 °C (lit.5b 230.1-230.6 °C): 1H NMR (500 MHz, DMSO-d6) δ 7.61 (d, J ) 7.3 Hz, 2H), 7.24 (m, 4H), 7.20 (m, 2H), 6.72 (br s, 1H), 3.24 (d, J ) 13.4 Hz, 2H), 2.07 (br s, 1H). (1aR,6β,10bR)-rel-1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclohepten-6-yl Benzoate (syn8). A solution of 4.19 g (16.2 mmol) of syn-4 in 100 mL of tetrahydrofuran was treated with 2.0 g (50 mmol, 60% mineral oil dispersion) of sodium hydride followed by 4.5 g (20 mmol) of benzoic anhydride. The mixture was heated to 60 °C for 1 h. The reaction mixture was poured into 70 mL of ethyl acetate and quenched with 70 mL of 1 M hydrochloric acid. The organic phase was washed with saturated aqueous sodium carbonate, dried with magnesium sulfate, and concentrated to a solid. The crude solid was purified by silica gel chromatography using a 3:2 mixture of heptane-1,2-dichloroethane as eluent to provide 3.04 g (55%) of syn-8 as a white solid, mp 230-231 °C: 1H NMR (500 MHz, CDCl3) δ 8.35 (d, J ) 7.3 Hz, 2H), 7.88 (s, 1H), 7.71 (t, J ) 7.3 Hz, 1H), 7.61 (t, J ) 7.7 Hz, 2H), 7.53 (dd, J ) 5.5, 4.7 Hz, 2H), 7.34 (dd, J ) 6.5, 4.2 Hz, 2H), 7.25 (m, 4H), 3.40 (d, J ) 13.2 Hz, 2H). Anal. Calcd for C23H16F2O2: C, 76.23; H, 4.45. Found: C, 75.93; H, 4.45. (1aR,6R,10bR)-rel-1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclohepten-6-yl Benzoate (anti8). A mixture containing 5.16 g (20 mmol) of syn-4, 3.17 g (26 mmol) of benzoic acid, and 6.55 g (25 mmol) of triphenylphosphine in 150 mL of tetrahydrofuran was cooled to -30 °C and treated with 5.05 g (25 mmol) of diisopropyl azodicarboxylate. (26) A diatomaceous silica filter aid.

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The mixture was allowed to warm, stirred at ambient temperature for 1 h, and then heated to 60 °C for 4 h. The reaction was cooled to ambient temperature and concentrated. The resulting solid was chromatographed over silica gel (heptane1,2-dichloroethane 3:2) to provide 5.00 g of a mixture of antiand syn-benzoates (anti-syn 2:1, NMR). A 1.5-g portion of the mixture was combined with 5 mL of 5 N sodium hydroxide and 10 mL of tetrahydrofuran. The resulting mixture was heated to 65 °C for 7 h and then cooled to ambient temperature. The mixture was partitioned by addition of 10 mL of tertbutyl methyl ether, and the organic phase was dried with magnesium sulfate and concentrated, affording 1.14 g of white solid containing the desired anti-benzoate and a mixture of anti- and syn-alcohols. Chromatography of the mixture (silica gel, heptane-1,2-dichloroethane 3:2) afforded 302 mg of anti-8 as a white solid, mp 162-164 °C: 1H NMR (500 MHz, CDCl3) δ 8.11 (d, J ) 7.2 Hz, 2H), 7.59 (t, J ) 7.5 Hz, 1H), 7.47 (t, J ) 7.5 Hz, 2H), 7.44 (d, J ) 6.8 Hz, 2H), 7.39 (d, J ) 7.6 Hz, 2H), 7.33 (d, J ) 7.5 Hz, 2H), 7.26 (d, J ) 7.7 Hz, 2H), 6.72 (s, 1H), 3.49 (d, J ) 12.5 Hz, 2H). Anal. Calcd for C23H16F2O2: C, 76.23; H, 4.45. Found: C, 75.92; H, 4.44. (1aR,6β,10bR)-rel-1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclohepten-6-ol (anti-4). A mixture of 220 mg (0.66 mmol) of anti-8, 2.0 mL of 1 N sodium hydroxide, and 2.0 mL of methanol was heated to 65 °C for 28 h. The reaction was partitioned by the addition of 8 mL of tertbutyl methyl ether. The organic layer was dried with sodium sulfate and concentrated, affording 157 mg (92%) of anti-4 as a white solid, mp 160 °C: 1H NMR (500 MHz, CDCl3) δ 7.36 (d, J ) 7.5 Hz, 2H), 7.28 (m, 2H), 7.22 (m, 4H), 5.51 (br s, 1H), 3.41 (d, J ) 12.6 Hz, 2H), 2.60 (br s, 1H). Anal. Calcd for C16H12F2O: C, 74.41; H, 4.68. Found: C, 74.12; H, 4.72. (1aR,6β,10bR)-6-Bromo-1,1-difluoro-1,1a,6,10b-tetrahydro-dibenzo[a,e]cyclopropa[c]cycloheptene (6). PBr3 method. To a mechanically stirred suspension of syn-4 (18.4 g, 71.2 mmol) in 150 mL of dichloromethane that had been cooled to 10-17 °C was added phosphorus tribromide (9.6 g, 35.6 mmol) dropwise over 15 min. The cooling bath was removed, and the reaction mixture was stirred for 2 h at ambient temperature. Analysis by gas chromatography indicated complete consumption of 4. Cold water (92 mL) and activated carbon (1.84 g) were added, and the resulting biphasic mixture was stirred for 30 min. The activated carbon was removed by filtration through Hyflo, and the layers were allowed to separate. The organic layer was washed twice with 184 mL of water and once with 184 mL of brine, dried over magnesium sulfate, and concentrated in vacuo to give 21.7 g (94.8%) of compound 6 as a light yellow foam. A 2.0-g portion was recrystallized from heptane, mp 120-122 °C: 1H NMR (300 MHz, CDCl3) δ 3.36 (s, 1H), 3.40 (s, 1H), 5.77 (s, 1H), 7.16-7.38 (m, 8H). Anal. Calcd for C16H11BrF2: C, 59.84; H, 3.45; Br, 24.88. Found: C, 59.96; H, 3.62; Br, 24.63. General Procedure for Studies of the Reaction of 6 with Piperazine. A mixture of compound 6 (50.0 mg, 0.156 mmol), piperazine (44.0 mg, 0.511 mmol), and the appropriate solvent (1.0 mL) was heated to 50 °C (thermostated oil bath) for 18 h. The mixture was cooled to room temperature, sampled, and analyzed by HPLC (Zorbax SB-CN column, λ ) 225 nm, 1.0 mL/min, 40 °C, 25 mM NaH2PO4, 0.1% TEA, pH 2.5) to determine isomer ratios. Results are shown in Table 1. (1aR,6R,10bR)-1-(1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclo-hepten-6-yl)pyridinium Bromide (anti-10). A mixture of 200 mg (0.623 mmol) of 6 and 3 mL of pyridine was heated at 50 °C for 5 h. The reaction was allowed to cool, effecting a (partial) crystallization of the product. The reaction was diluted with 5 mL of tert-butyl methyl ether (MTBE), and the crystals were collected by filtration, washed with MTBE, and dried to yield 260 mg (100%) of anti-10 (monohydrate) as a tan solid, mp 207-208 °C: 1H NMR (500 MHz, CDCl3) δ 8.65 (d, J ) 6.6 Hz, 2H), 8.54 (t, J ) 7.6 Hz, 1H), 8.09 (t, J ) 7.2 Hz, 2H), 8.00 (m, 3H), 7.45 (m, 2H), 7.40 (m, 4H), 2.65 (d, J ) 12.6 Hz, 2H). Anal.

Improved Synthesis of LY335979 Trihydrochloride Calcd for C21H16BrF2N‚H2O: C, 60.30 H, 4.34, N, 3.35. Found C, 60.68; H, 4.35, N, 3.37. (1aR,6R,10bR)-1-(1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclohepten-6-yl)pyrazinium Bromide (11). To a stirred slurry of 27.3 Kg (105.7 mol) of syn-4 in 220 L of dichloromethane was added 24.1 Kg (143.0 mol) of 48% aqueous HBr. The resulting slurry was heated to reflux for 22 h with azeotropic removal of water via a DeanStark separator. After the mixture cooled to 20-25 °C, 14.0 Kg of anhydrous sodium sulfate and 7.0 Kg of activated carbon were added. The mixture was stirred at 20-25 °C for 1 h and filtered with Hyflo, and the filter cake was washed with 2 × 60 L of dichloromethane. The combined filtrate and washes were distilled (40-45 °C, atmospheric pressure) to provide a solution of 6 in 150 L of dichloromethane. To this solution was added 32.4 Kg (404.5 mol) of pyrazine followed by 16.5 L of dimethyl sulfoxide, and the resulting solution was heated to 30 °C for 25 h. The resulting yellow-orange suspension was diluted with 180 L of ethyl acetate, and the mixture was stirred at 20-25 °C for 2 h to complete crystallization of the product. The crystals were filtered, washed with 180 L of ethyl acetate, and dried in vacuo at 40 °C to provide 35.5 Kg (88%) of 11 as a light yellow crystalline solid, mp 165 °C: 1H NMR (500 MHz, DMSO-d6) δ 9.46 (d, J ) 2.7 Hz, 2H), 8.77 (t, J ) 1.7 Hz, 2H), 7.74 (d, J ) 7.5 Hz, 2H), 7.42-7.55 (m, 6H), 7.27 (s, 1H), 3.19 (d, J ) 12.6 Hz, 2H); 13C NMR (126 MHz DMSO-d6) δ 152.5, 135.8, 135.4, 134.4, 133.2, 132.1, 129.9, 129.6, 112.9, 110.6, 108.3, 77.4, 28.7, 28.6; FD MS m/e 321 (M - Br). Anal. Calcd For C20H15BrF2N2: C, 59.87; H, 3.77; N, 6.98. Found: C, 59.84; H, 3.66; N, 6.83. (1aR,6R,10bR)-1-(1,1-Difluoro-1,1a,6,10b-tetrahydrodibenzo[a,e]cyclopropa[c]-cyclohepten-6-yl)-piperazine Hydrochloride (anti-2 HCl). To stirred slurry of 35.4 Kg of 13 (88.2 mol) in 185 L of EtOAc was added trifluoroacetic acid (34.6 Kg, 303.5 mol). To this mixture was added a 2.0 M solution of lithium borohydride in THF (59.6 Kg, 66.5 L, 133.0 mol) over 1.5 h while maintaining the reactor temperature between 10 and 20 °C. The reaction mixture was stirred at 20-25 °C for 2 h. The reaction solution was added carefully to 351 Kg of 10% (w/w) aqueous potassium carbonate solution over 15 min while maintaining the vessel temperature below 25 °C. The mixture was stirred at 20 °C for 30 min, and the layers were separated. The organic phase was washed with 2 × 300 Kg of 10% (w/w) aqueous potassium carbonate solution and once with 185 Kg of 15% (w/w) aqueous sodium chloride solution and dried over 53.4 Kg of anhydrous sodium sulfate. After filtering the drying agent, 8.8 Kg (1.0 equiv) of 37% aqueous HCl was added (15-20 °C) over 35 min, and the resulting slurry was stirred at 20 °C for 9 h. The precipitate was filtered, washed with 100 L of ethyl acetate, and dried in vacuo (45 °C) to provide 24.7 Kg of anti-2 HCl (85.6%, or 21.1 Kg as anti-2 (HPLC assay), 66% yield), mp 274-278 °C (dec): 1 H NMR (500 MHz, DMSO-d6) δ 9.41 (br s, 2H), 7.17-7.31 (m, 8H), 4.17 (s, 1H), 3.52 (d, J ) 12.4 Hz, 2H), 3.11 (br s, 4H), 2.48-2.51 (m, 4H); 13C NMR (126 MHz, DMSO-d6) δ 142.3, 133.4, 130.5, 129.6, 129.0, 128.4, 115.9, 113.6, 111.3, 76.2, 49.0, 43.6, 29.2, 29.1, 29.0; FD MS m/e 326 (M+). Anal. Calcd for C20H21ClF2N2: C, 66.20; H, 5.83; N, 7.72. Found: C, 66.08; H, 5.90; N, 7.72. 5-[(2R)-Oxiranylmethoxy]-quinoline (3). To a 0 °C suspension of 18.5 Kg (127.3 mol) of 5-hydroxyquinoline in 231 L of THF was added 15.1 Kg (127.3 mol) of potassium tertbutoxide (95% potency) in three portions, and the resulting thick slurry was stirred for 1 h at 20-25 °C. A solution of 33.0 Kg (127.3 mol) of (R)-glycidyl nosylate in 83 L of THF was then added over 1 h. The reaction mixture was stirred for 16 h at 23-26 °C, at which time HPLC analysis indicated that the reaction was complete. The reaction mixture was concentrated (50-100 mmHg) to about 200 L. A 440-L quantity of toluene was added, and the mixture was concentrated (50 mmHg) to a volume of about 200 L. Another 130 L of toluene

were added, and the mixture was stirred for 30 min at 20-25 °C. The resulting inorganic precipitate was filtered and washed with 200 L of toluene. The combined toluene fractions were washed with a solution of 5.1 Kg (63.7 mol) of 50% aqueous NaOH in 330 L of water, and the aqueous layer was backextracted with 130 L of toluene. The combined toluene layers were washed with 130 L of water, and approximately 160 L of toluene was distilled off to effect azeotropic drying of the solution. Basic alumina (16.5 Kg) was added to the dried yellow-orange toluene solution, and the mixture was stirred for 30 min at 20-25 °C. The alumina was filtered and washed with 200 L of toluene. The combined filtrate and wash were concentrated (50 mmHg) to about 100 L and heated to 45-55 °C. Heptane (500 L) was then added at such a rate to maintain the temperature at >45 °C. The solution was allowed to cool to 40 °C and was seeded. The crystallizing mixture was cooled to 0 °C over 2 h and then stirred at 0-5 °C for an additional 2 h. The crystals were filtered, washed with 100 L of heptane, and dried in vacuo (25 °C) to provide 19.1 Kg (74%) of 3 as a crystalline solid, mp 79-81 °C, 98.6% ee (chiral HPLC):27 1H NMR (500 MHz, CDCl3) δ 2.83 (dd, J ) 4.8, 2.7 Hz, 1H), 2.97 (m, 1H), 3.48 (m, 1H), 4.10 (dd, J ) 11.0, 6.0 Hz, 1H), 4.43 (dd, J ) 11.0, 2.7 Hz, 1H), 6.85 (d, J ) 7.8 Hz, 1H), 7.38 (dd, J ) 8.5 Hz, 4.1 Hz, 1H), 7.59 (m, 1H), 7.71 (d, J ) 8.5 Hz, 1H), 8.61 (m, 1H), 8.90 (m, 1H); 13C NMR (CDCl3, 75.5 MHz) δ 153.9, 150.8, 149.1, 130.8, 129.2, 122.2, 120.8, 120.3, 105.3, 69.3, 50.0, 44.6. [6(R)-(1aR,6R,10bR)]-4-(1,1-Difluoro-1,1a,6,10b)tetrahydrodibenzo[a,e]cyclopropa[c]cyclohepten-6-yl)-R-[(5-quinolinyloxy)methyl]-piperazineethanol, Trihydrochloride Salt (1). A suspension of 20.3 Kg of 2 hydrochloride (87% as 2, 48.9 mol) and 10.3 Kg (99.7 mol) of powdered sodium carbonate in 340 L of ethanol was stirred at 20-25 °C for 1.5 h. Addition of 9.83 Kg (48.9 mol) of 3 was completed in one portion, and the reaction mixture was heated to 60-70 °C for 36 h. The mixture was cooled to 20-25 °C, filtered through a 46-Kg plug of silica gel, and eluted with an additional 400 L of ethanol. The combined filtrate and washes were distilled at 45-55 °C (170-180 mmHg) to a volume of approximately 265 L and then heated to 60-70 °C with stirring. An 88-Kg solution of HCl (3.28 N in ethanol) was added over 35 min and transferred with 10 L of anhydrous ethanol. The solution was seeded, causing the trihydrochloride salt to precipitate. The mixture was cooled to 20-25 °C over 2 h and stirred at that temperature for 15 h. The precipitate was filtered onto a filter dryer, washed with 105 and 30 L of ethanol, and partially dried on the filter. Methanol (200 L) was heated to 50-60 °C and added to the wet cake to dissolve the crude product on the filter and transfer the solution to another vessel. An additional 170 L portion of methanol was used to complete the transfer. The solution was distilled at 35-45 °C and 200300 mmHg to a volume of approximately 200 L. The mixture was again heated to 60-65 °C for 3 h to dissolve all solids and then was cooled to 20-25 °C over 30 min. The suspension was stirred for 3 h, and then 590 L of ethyl acetate were added to complete the crystallization. After stirring for 14 h at 2025 °C, the precipitate was filtered, washed with 210 L of ethyl acetate, and dried in vacuo at 45 °C to provide 26.0 Kg (74.6%) of 1 as a light yellow crystalline methanol solvate. The solvate was converted to a crystalline hydrate (xH2O) by equilibration in moist nitrogen. The hydrated crystals were correlated by physical and pharmacological data with material prepared at the Syntex laboratories.

Acknowledgment. We gratefully acknowledge the contributions made by Jason Cronin, Ch.E., Jennifer Flynn, Ch.E., Brittany Long, Ch.E., Mark Pittman, Ch.E., Bruce Parker, Ch.E., and Jeff Vicenzi, Ch.E. (27) A sample prepared under similar conditions showed an ee of 99.2% with an optical rotation of [R]25D -36.4 (c 2.10, EtOH), lit.7 [R]23D -35.6.

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Barnett et al. Supporting Information Available: Table of 1H NMR data for 1,1-difluoro-1,1a,6,10b-tetrahydrodibenzo-[a,e]cyclopropa[c]-cyclohepten-6-yl derivatives, 1H NMR spectra for syn and anti compounds 4 and 8 and NOE spectra for syn and anti compounds 8 and 10, and a table relating efficiency for

7660 J. Org. Chem., Vol. 69, No. 22, 2004

the conversion lithium chlorodifluoroacetate to temperature in difluorocyclopropanation. This material is available free of charge via the Internet at http://pubs.acs.org. JO049051V